Thibaud Hug de Larauze is waving his iPhone, boasting that it is more than seven years old. “It works great,” he says. Not what you’d expect from a tech entrepreneur heading one of France’s biggest “unicorn” startups – Back Market – which has raised more than $1bn to expand into 18 countries.The chief executive of the secondhand gadget marketplace says he would rather identify as an eco-warrior than a tech guru, fighting to persuade us all to buy pre-owned phones, laptops and other devices, and ...